This application is based on and incorporates herein by reference Japanese Patent Applications No. 2001-397543 filed on Dec. 27, 2001 and No. 2002-312615 filed on Oct. 28, 2002.
The present invention relates to a semiconductor device in which a semiconductor chip generating heat is located between a pair of heat sinks and to a method for manufacturing the device.
A semiconductor chip for controlling large electric power and current generates so much heat in use that a proposed semiconductor device including the chip includes a pair of heat sinks, which are made of a metal such as copper and aluminum, to efficiently release the heat generated by the chip. As shown in FIG. 1, in a proposed semiconductor device 1, a semiconductor chip 2 and a coupler 5 are located between a first heat sink 3, or a lower heat sink 3, and a second heat sink 4, or an upper heat sink 4. The upper heat sink 4 and the coupler 5, the coupler 5 and the chip 2, and the chip 2 and the lower heat sink 3 are respectively connected by solders.
The upper and lower heat sinks 4, 3 also function as electrodes for the semiconductor chip. A mold resin 6 is located between the heat sinks 3, 4 to seal the chip 2, the coupler 5, and the solders. As illustrated in FIG. 1, the upper and lower heat sinks 4, 3 are respectively exposed on the lower surface and the upper surface of the device 1. Therefore, the upper and lower heat sinks 4, 3 efficiently transmit and release the heat generated by the chip 2 while being insulated partly by the mold resin 6.
As shown in FIG. 2, the semiconductor device 1 is located in use between a cooling member 7 and a U-shaped metal fixer 9, which is connected to the cooling member 7 by male screws 10. Two insulating sheets 8 are respectively located between the cooling member 7 and the device 1 and between the device 1 and the metal fixer 9. The cooling member 7 is made of a metal such as copper and aluminum, which can efficiently transmit and release heat. Although not illustrated, the cooling member includes a cooling water passage. The metal fixer 9 is made of a metal such as copper and aluminum. The insulating sheets 8 needs to be made of an insulating material that is thermally conductive and elastically shrinkable.
In the semiconductor device 1, the upper and lower heat sinks 4, 3 are exposed, so the insulating sheets 8 are needed to insulate the exposed surfaces and the metal fixer 9 is needed to transmit the heat generated by the chip 2 from the upper heat sink 4 to the cooling member 7. Therefore, the structure of the assembled article shown in FIG. 2 is relatively complicated, and the manufacturing cost of the assembled article is relatively high.
In addition, the thickness of the semiconductor device 1 deviates to some degree. Therefore, when the semiconductor device 1 is fixed to the cooling member 7 with the metal fixer 9, it is difficult to control the force with which the metal fixer 9 presses the device 1 against the cooling member 7. When the thickness of the semiconductor device 1 deviates too much from a predetermined value, the semiconductor device 1 breaks or is not firmly fixed to the cooling member 7. If only the insulating sheets 8 absorbed the force enough, the above problem could be solved. However, no material that is elastically shrinkable enough to be used for the insulating sheets 8 has been available yet.
Moreover, in the semiconductor device 1, the heat generated by the semiconductor chip 2 is partially transmitted from the upper heat sink 4 to the cooling member 7 through one of the insulating sheets 8 and the metal fixer 9. Therefore, the heat transmission path through the upper heat sink 4 is much longer than that through the lower heat sink 3, so the upper heat sink 4 releases the heat less efficiently than the lower heat sink 3.
The present invention has been made in view of the above aspects. A first object of the present invention is to reduce the manufacturing cost of a semiconductor power device by simplifying the means for insulating a heat sink and the means for releasing heat from the heat sink. A second object of the present invention is to improve the heat releasing capability of the heat sink.
In the present invention, a semiconductor device includes a semiconductor chip, a first heat sink, a second heat sink, and a mold resin. The first heat sink is electrically and thermally connected to a surface of the semiconductor chip for functioning as an electrode for the semiconductor chip and releasing the heat generated by the semiconductor chip. The second heat sink is electrically and thermally connected to another surface of the semiconductor chip for functioning as another electrode for the semiconductor chip and releasing the heat. The semiconductor chip and the heat sinks are covered with the mold resin such that the heat sinks are exposed on a substantially flat surface of the mold resin.
With the above structure, the means for insulating the heat sinks and releasing heat from the semiconductor chip become simple, so the device is preferably cost-effective in the manufacturing and has preferable heat releasing capability.